The invention relates to an apparatus for recycling solvent of the type utilized in dry-cleaning machines and in other similar machinery or equipment.
As one having ordinary skill in the art will be aware, the majority of dry-cleaning machines utilizing solvent, such as perchloroethene, incorporate a system capable of recycling such solvent following one or more cleaning cycles.
Recycling of the solvent is essential if the cost of cleaning is to be kept within competitive limits, and must be carried out according to a precise technique and in an efficient manner in order to avoid pollution of drains and sewers by the waste solvent, and to ensure that vapor given off by the solvent does not contaminate the environment where the machine is sited.
Recycling of solvent comes about as follows: water and solvent mingled during the cleaning cycle are fed into a chamber fitted with heater elements, and are vaporized, whereupon the vapor given off distils in a condenser. The liquid produced flows into a separator which draws off the water and channels the solvent back into the machine. Impurities collected by the liquid during cleaning remain in the chamber.
The above process is efficient enough as regards production of purified solvent for recycling purposes, but is considerably expensive and time-consuming. Such a process also jeopardizes service-life of the apparatus, since heat generated in the chamber for evaporation of the mingled water and solvent (perchloroethene in particular) is wasted entirely, and what is more, dictates the requirement for a copious flow of water by means of which to cool the condenser. Moreover, time available in which to evaporate the liquid is relatively short, and substantially the same amount of heat must be generated for each recycle, and the same time-lapse allowed, in order to distil the bulk of mingled water and solvent in its entirety.
The most serious drawback, however, in systems of the type described, is that relatively high temperatures are produced in the chamber due to the use of electric immersion heaters and the like: for example, the boiling point of pure perchloroethene, 121.degree. C., will be reached easily in the chambers of such conventional systems, and temperatures of this order, combined with the characteristics of the mingled water and solvent being distilled, represent a marked corrosion hazard to the walls of the chamber. When mingled, water and chlorine give place to acidity, as water permits the formation of free chlorine ions; in practical terms, the water becomes a `vehicle` for acidity, a minus factor which increases a magnitude the higher the temperature.
Damage to the chamber walls is made still worse by the thermal shock produced on introduction thereinto of a fresh batch of liquid, which enters at room temperature substantially, no sooner than the previous recycle has terminated and the chamber walls are still invested with heat of the order mentioned above. This terminal shock gives place to a further shock which occurs in the system's internal pressure, since the sudden temperature drop occasions immediate condensation of such vapor as still remains in the chamber, producing a depression in the chamber itself, and although conventional systems of the type incorporate valves to offset the pressure drop by drawing-in air from the environment, such a remedy is negative in practice by reason of the fact that small though nonetheless damaging emissions of solvent vapor are let out into the environment during recycle.
It is a fundamental object of the invention, in view of the state of the art, to provide an apparatus for the recycling of solvent utilized in dry-cleaning machines and similar equipment such as will avoid the drawbacks described above.